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The final examination questions for mathematics 400 at the university of british columbia, december 2005. The examination covers nonlinear pdes, polar coordinates, heat conduction, and the telegraph equation. Students are required to find solutions, provide plots, and determine eigenvalues and eigenfunctions.
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The University of British Columbia Final Examination - December 9, 2005 Mathematics 400 Instructor: Dr. A. Cheviakov
Closed book examination Time: 2.5 hours
Name Signature
Student Number Section 101 102 (circle one)
Special Instructions:
Rules governing examinations
Total 100
Page 1 of 7
[15 pts] Problem 1. Find the solution y(x, t) of the nonlinear PDE problem
yt + (1 − 3 y^2 )yx = 0 − ∞ < x < +∞, t > 0
y(x, 0) =
2 / 3 , x < 0; 0 , x > 0.
Provide a plot showing characteristics.
[20 pts] Problem 3. Consider heat conduction problem in a 2D infinite strip of width H.
ut = k(uxx + uyy), 0 < y < H, − ∞ < x < +∞, t > 0
uy(x, 0 , t) = uy(x, H, t) = 0, u(x, y, 0) = f (x, y).
Here u(x, y, t) is temperature, and f (x, y) a smooth function absolutely integrable in the strip. (i) Solve the problem to find u(x, y, t) for t > 0. (ii) Find the equilibrium heat distribution as t → ∞. (iii) Find the exact form of the solution, if f (x, y) = e−x 2 sin(2πy/H).
[25 pts] Problem 4. Consider the Linear Telegraph Equation problem:
uxx(x, t) = αutt(x, t) + βut(x, t) + γu(x, t), x > 0 , t > 0
u(0, t) = f (t), u(x, 0) = ut(x, 0) = 0.
Here α, β, γ ≥ 0 are constants. This PDE problem describes electromagnetic signal transmission along a semi-infinite cable; x is a coordinate along the cable, and t ≥ 0 time. u(x, t) is bounded for all x, t > 0.
(i) Find the Laplace transform (in time) U (x, s) of the solution u(x, t). (ii) Suppose β^2 = 4αγ. Find the solution u(x, t). Write it in the form that explicitly contains necessary Heaviside function(s). (iii) Verify by substitution that your solution satisfies the initial-boundary value problem. (iv) Specify another set of constants α, β, γ (β^2 6 = 4αγ), for which the solution u(x, t) can be explicitly found. Find it.